Skill Needed Item level Disenchants into (Superior/blue and above items DE into the rare essence/shards more often)
1..................1-15........Strange Dust (Lesser/Greater Magic Essence, Small Glimmering Shard)
25...............16-20........Strange Dust (Lesser Astral Essence, Small Glimmering Shard)
50...............21-25........Soul Dust (Greater Astral Essence, Large Glimmering Shard)
75...............26-30........Soul Dust (Lesser Mystic Essence, Small Glowing Shard)
100.............31-35........Vision Dust (Lesser/Greater Mystic Essence, Large Glowing Shard)
125.............36-40........Vision Dust (Lesser Nether Essence, Small Radiant Shard)
150.............41-45........Dream Dust (Greater Nether Essence, Large Radiant Shard)
175.............46-50........Dream Dust (Lesser Eternal Essence,Small Brilliant Shard)
200.............51-55........*^ Illusion Dust (Greater Eternal Essence, Large Brilliant Shard)
225.............56-60(59?).+^ Illusion Dust
250.............61-65........??
275.............66-70........??

* Nexus Crystals from Superior/blue and above 51-60 items only?
+ 56-60 greens only make Illusion Dust?
+ 56-60 blues only make Large Brilliant Shard?
+ 56-60 Epics only make Nexus Crystals?
^ Old world gear DEs into Illusion/Eternal/Brilliant and BC gear into Arcane/Lg Prism?

The disenchant skill appears in your spellbook when you learn enchanting.

You only get skill from disenchanting items up to 50 skill. This was not changed with the patch that limited item levels you could DE based on your skill, so even high level items won't give skill for DEing after you reach 50 skill.

You used to be able to disenchant high level items with low enchanting skill, this was changed around the time of the Burning Crusade release.

You can disenchant soulbound items that are bound to the enchanter, other people's soulbound items can not be disenchanted, even in the 'Will not be Traded' window.

AFAIK only most equippable items above white can be disenchanted, no recipes. There are some equippable items that can not be disenchanted (Twilight Clutists set for one)

Вот что нашёл по ДезЭнчанту... (кто хорошо знает буржуйский, переведите)